RELAXATION OF RAT THORACIC AORTA INDUCED BY PYRIDINE

The pharmacological and toxicological activity of pyridine was determi ned in rat thoracic aorta. Pyridine inhibited norepinephrine (3 mu M)- induced phasic and tonic contractions in the thoracic aorta as well as the endothelium-denuded aorta of the rat. The tonic pre-contraction e licited by norepinephrine was also relaxed by the addition of pyridine and this relaxing effect was not affected by indomethacin (20 mu M), N-G-monomethyl-L-arginine acetate (50 mu M) or methylene blue (50 mu M ). In high-K+ medium (80 mM), pyridine inhibited the Ca2+ concentratio n-dependent vasocontraction. Moreover, in Ca2+-free medium, the norepi nephrine (3 mu M)-induced phasic contraction was also suppressed by py ridine, while the caffeine (10 mM)-induced contraction remained unaffe cted. The cAMP and cGMP levels of rat aorta were not changed by pyridi ne. The Ca-45(2+) influx elicited by either norepinephrine or high-Kwas inhibited by pyridine in a concentration-dependent manner. All of these findings indicated that pyridine relaxes rat thoracic aorta by v irtue of its Ca2+ channel-blocking properties in vascular smooth muscl e.